The present invention relates to a driving apparatus for driving an inking device or dampening unit arranged in the printing unit of a multicolor printing press or a perfector.
In a multicolor printing press, depending on the number of colors to be printed, all the printing units need not be driven, and sometimes only some of a plurality of printing units are driven. In this case, in order to stop driving an inking device or dampening unit in a printing unit which is not to be driven, a driving connecting/disconnecting means for connecting/disconnecting a driving source to/from the inking device or dampening unit is provided to each printing unit.
In order to prevent degradation of the quality of the printing product, the relationship between the phase of a plate cylinder and the phase of an ink reciprocating roller during disconnection effected by the driving connecting/disconnecting means must be correctly reproduced during connection. For this purpose, as shown in Japanese Utility Model Registration No. 2537504, a conventional multicolor printing press includes a rotary encoder which detects the phase of the reciprocating motion of an ink reciprocating roller and the phase of a plate cylinder during disconnection effected by a driving connecting/disconnecting means, and a controller which stores the detected phases.
FIGS. 12 to 15 show a driving connecting/disconnecting mechanism employed by a driving apparatus in a conventional printing press. Referring to FIG. 12, a driving gear 106 axially mounted on the end shaft of a plate cylinder is connected to a printing press motor serving as a driving source. When the printing press motor is driven, the plate cylinder rotates through the driving gear 106. A first gear 111 is rotatably, axially supported by a shaft 114 extending perpendicularly from a frame 102, such that the movement of the first gear 111 in the axial direction is regulated.
The first gear 111 has 34 teeth 111a which constantly mesh with 70 teeth 106a of the driving gear 106. Four first engaging projections 111b are formed on the side surface of the first gear 111 equiangularly in the rotational direction of the first gear 111. A tooth-to-tooth angle θ2 (FIG. 14C) between the two adjacent teeth 111a of the first gear 111 and a projection-to-projection angle θ1 (FIG. 14B) between the two adjacent engaging projections 111b are largely different from each other. The angle θ2 is not an integer multiple of the angle θ1.
Referring to FIG. 12, a second gear 112 is rotatably and axially movably supported by an end 114a of the shaft 114 such that it is axially supported to be coaxial with the first gear 111. Teeth 112a which constantly mesh with teeth 124a of a driven gear 124 are formed on the circumferential surface of the second gear 112, and engaging projections 112b which engage with the engaging projections 111b of the first gear 111 project from the side surface of the second gear 112. As shown in FIG. 14A, the four engaging projections 112b are provided equiangularly with an angle θ1 in the circumferential direction. The driven gear 124 meshes with a gear (not shown) that drives the ink roller of the inking device. When the printing press motor is driven, the plate cylinder rotates, and simultaneously the ink roller is driven in synchronism through the driving gear 106, first and second gears 111 and 112, and driven gear 124.
Referring to FIG. 12, an air cylinder 113 is attached, through an auxiliary bracket 117, to a bracket 116 fixed to oppose the frame 102. The second gear 112 is mounted on a rod 118 which is driven by the air cylinder 113 to move reciprocally. In this arrangement, when the rod 118 of the air cylinder 113 moves forward, the engaging projections 112b of the second gear 112 engage with the engaging projections 111b of the first gear 111. When the rod 118 of the air cylinder 113 moves backward, the engaging projections 112b of the second gear 112 and the engaging projections 111b of the first gear 111 disengage from each other.
In the former prior art, the driving source and the ink reciprocating roller are connected to and disconnected from each other by an electromagnetic clutch. Therefore, to transmit driving accurately, the surface pressures of clutch plates must be high. This increases the capacity of the electromagnetic device, leading to a high cost.
In the latter prior art, the driving force is transmitted by engaging the engaging projections 111b and 112b of the first and second gears 111 and 112, respectively, with each other. In this case, as the pressure of the air of the air cylinder 113 can be decreased comparatively low, the cost does not become high. However, the number (34) of teeth 111a of the first gear 111 and the number (70) of teeth 106a of the driving gear 106 that meshes with the first gear 111 are different from each other. Thus, after the first and second gears 111 and 112 are disconnected from each other, when they are to be connected again, their engaging projections 111b and 112b cannot engage with each other again.
This will be described. Immediately after the first and second gears 111 and 112 are disconnected, the four engaging projections 112b of the second gear 112 shown in FIG. 14A and the engaging projections 111b of the first gear 111 shown in FIG. 14B are in such a phase that they can engage with each other. At this time, the hatched tooth 111a in FIG. 14C shows the expedient disconnecting phase in the rotational direction of the first gear 111.
While the first and second gears 111 and 112 are disconnected from each other, because the driving gear 106 rotates, the first gear 111 meshing with the gear 106 also rotates. When the first and second gears 111 and 112 are to be connected to each other again, the printing press motor is stopped at a phase of the plate cylinder which is the same as that for disconnection. Thus, the driving gear 106 is stopped at the same phase as that for disconnection.
The number of teeth of the driving gear 106 and that of the first gear 111 meshing with the driving gear 106 are different. Thus, sometimes the teeth 111a of the first gear 111 are not located at the same phase as that for disconnection. In other words, the number i of revolutions of the first gear 111 per revolution of the plate cylinder 1 is 70/34. Even when the driving gear 106 is located at the same phase as that for disconnection, the first gear 111 is not located at the disconnection phase nearly always. In this case, the teeth 111a stop at positions shifted by a phase which is an integer multiple of the angle θ2.
Accordingly, the engaging projections 111b of the first gear 111 also stop at the phase shifted from the disconnection phase by an angle which is an integer multiple of the angle θ2 (FIG. 14B). As described above, the angle θ1 is different from the angle θ2, and the angle θ2 is not an integer multiple of the angle θ1. Thus, the phase of the engaging projections 111b of the first gear 111 stopped at the phase shifted by the integer multiple of the angle θ2 is located at a phase different from the disconnection phase. For this reason, the phase of the engaging projections 111b of the first gear 111 do not match the phase of the engaging projections 112b of the second gear 112, and the engaging projections 111b and 112b cannot engage with each other again.